Mass produced hollow articles of glassware, such as bottles, jars and the like (hereinafter referred to as bottles) are usually produced by glass forming machines which are typically formed by combining a number of individual sections. Each individual section (IS or Section) is capable of manufacturing one to four bottles at a time. By combining numerous Sections in a single integrated glassware forming machine, an increased output capacity for mass producing bottles is achieved.
A bottle is formed from a measured volumetric quantity of molten glass, called a gob. One gob is delivered to each Section for each bottle which is produced. The capacity of a Section is rated in terms of the number of gobs which it is capable of forming into bottles simultaneously. For example, a triple gob IS machine is capable of producing simultaneously three bottles at a time.
The process of forming mass produced bottles begins when gobs are deposited initially into cavities of a blank mold of each Section. Each gob is formed into a first configuration called a parison in the blank mold. A parison includes a finish, which generally refers to the fully formed neck and mouth of the bottle, and a remaining body. Both the finish and the body assume an external configuration established by the shape of the cavity of the blank mold. The parison also includes an initial interior opening extending through the finish and somewhat into the body of the parison. Pressurized air is later supplied to the initial opening to expand the body of the parison into the final completed shape of the bottle.
A plunger mechanism forms the initial opening through the finish and into the fluid glass body of the parison while it is within the blank mold cavity. Thereafter the blank mold separates and the parison is transferred by an invert arm to another mold of the IS called a blow mold. In the blow mold, the fluid glass body of the parison is expanded by forcing pressurized air into the initial opening, thereby expanding the fluid glass body into the final body shape defined by the configuration of the blow mold. The bottle is thereafter removed from the blow mold and transferred onto a conveyor, which transports the bottle to other equipment for further heat treatment to complete its manufacture.
Each I.S. machine, therefore, receives the gobs of molten glass, initially forms each gob into a parison, subsequently blows each parison into the completed bottle shape, and transfers the bottle thus formed on for completion. This process repeats itself very rapidly, and it is by this process that large numbers of glass articles are produced.
IS machines are either of a blow-and-blow type or a press-and-blow type. These designations refer to the two types of operations which first form the initial opening in the parison in the blank mold and which thereafter expand the initial opening to complete the shape of the body of the bottle in the blow mold. In a blow-and-blow operation, the initial opening in the parison is formed by blowing pressurized air into a small cavity formed by a plunger tip residing in the fluid glass. After the parison is transferred to the blow mold, pressurized air is blown into the initial opening to complete the bottle shape. In a press-and-blow operation, the initial opening is completely formed by the mechanical action of pressing a ram-like plunger member into the fluid glass. After the parison is transferred to the blow mold, pressurized air is blown into the initial opening to complete the body shape. Thus, in a blow-and-blow operation, the initial opening is completed by blowing air into a small cavity to expand the cavity into the initial opening, while in a press-and-blow operation, the initial opening is formed entirely by mechanical movement.
A conventional plunger mechanism comprises a piston and cylinder assembly which is positioned directly beneath the blank mold of each IS. The plunger tip or the ram-like plunger member is typically attached to the end of a shaft connected to a piston. Mechanical springs and compressed air supplied to the interior of the cylinder combine to move the piston and thereby extend and retract the plunger tip or member at predetermined intervals during the formation of the parison. At the start of the parison forming process, a thimble of the plunger mechanism extends upward to contact a neck ring mechanism held by an invert arm to align the plunger tip or ram-like member with the blank mold cavity. A spring typically biases the thimble in its upward position, thereby establishing a "load" position in which the gob is received in the blank mold cavity. The load position is common to both the blow-and-blow and press-and-blow operations, but the remaining steps in the formation of the parison differ in the blow-and-blow and press-and-blow operations.
In the prior art blow-and-blow operation, pressurized air is applied to the piston simultaneously with the extension of the thimble to extend the plunger tip through the thimble and upward to a maximum height within the blank mold. While the plunger tip is in this "up" position, pressurized air ("settleblow air") is supplied from the top of the blank mold cavity to press the molten glass gob around the extended plunger tip to form the finish. The plunger is then lowered to an intermediate or "counterblow" position by relieving the previously applied air pressure on the piston and allowing a second spring, which was compressed by the movement of the piston to the "up" position, to expand and move the piston and attached plunger tip down to the counterblow position. Movement of the plunger from the "up" position to the "counterblow" position forms a small cavity. The small cavity is then expanded into the initial opening by blowing pressurized air past the plunger tip while in the counterblow position. Thereafter, air pressure is applied to the piston to fully retract both the plunger tip and thimble. In this last "transfer position," the first spring is once again compressed. The transfer position allows the formed parison to be moved by the invert arm to the blow mold.
The prior art press-and-blow operation employs a different sequence of plunger positions. In the "load" position, springs bias the thimble into contact with the neck ring mechanism. In addition, springs also bias the piston upward to position the plunger ram member in an intermediate position in which the plunger ram member extends partially into the blank mold cavity. The gob is transferred into the blank mold cavity while the plunger ram member is in the load position. Pressurized ("settleblow") air is applied from the top of the blank mold cavity to force the gob downward. Pressurized air is then applied to the piston to extend the plunger ram member upward to its highest position. The upward movement of the plunger ram member presses the fluid glass to establish the finish and the shape of the parison while simultaneously forming the initial opening within the parison. Thereafter, the plunger ram member is withdrawn from the blank mold cavity by applying compressed air to the top side of the piston to move the piston downward and compress the spring below the piston. Once the plunger has returned to its lowermost position, the parison is transferred to the blow mold. When the compressed air to the top of the piston is relieved, the compressed spring will expand and move the plunger to its intermediate load position for the start of the next cycle during which a gob will be transformed into a parison.
The use of springs in the plunger mechanism to achieve the desired positions of the plunger tip or ram member in both the blow-and-blow and press-and-blow operations are prone to cause certain undesirable effects. The movement obtained from springs cannot be controlled precisely, both in terms of speed and consistency of position. The driving movement of the springs also tends to create a hammering effect between mechanical components which leads to stress and a tendency for failure of the affected components. Further, spring movement may be characterized by slight inconsistencies in timing and somewhat varied movement positions. Additionally, springs are susceptible to thermal effects due to the relatively high temperature of the molten glass gobs and the surrounding equipment of the glass forming machine. The thermal effects may create inconsistencies in both the length of the spring and the force it applies. These effects, resulting from the springs used in the prior art plunger mechanisms, can result in inconsistencies in forming the parison. Even slight inconsistencies may cause deformities in the finished bottle or other glassware article.
Furthermore, the repetitious mechanical contact of the components created by the springs moving the components of the plunger mechanism together and against one another has the tendency to create accelerated wear and fatigue on the plunger mechanism elements. The springs are also susceptible to fatigue and failure from repeated cycling, thus creating a risk of unpredictable mechanical failure. Consequently, plunger mechanisms require frequent repair and replacement of failed component parts. Of course, during times of plunger mechanism repair, the individual section must be removed from service and is therefore unavailable for the production of bottles.
Conventional plunger mechanisms are typically positioned and aligned beneath the blank mold cavities by an adjustable foot extending to the floor or the bottom of the IS machine. The adjustable foot allows the plunger mechanism to be raised or lowered to accommodate blank molds and plunger mechanisms of various sizes according to the size and shape of the bottle being produced. The adjustable foot is also used to establish the initial alignment of the plunger mechanism with the blank mold cavity.
The adjustable foot also tends to cause the prior art plunger mechanism to slip out of alignment with the blank mold cavity. The effects of thermal expansion and vibration of the I.S. machine can result in relative movement between the single alignment point at the foot and the blank mold cavity. Even slight misalignments can create deformities and unacceptable weak spots in the completed bottles.
The adjustable foot also makes repair and replacement of the plunger mechanism difficult. Mechanical failures of the elements of the plunger mechanism, and changes in the type and size of glassware produced, cause frequent removals of the conventional plunger mechanisms for repair or replacement. The adjustable foot necessitates that each replaced plunger mechanism undergo a tedious and time consuming realignment process when it is installed, which increases down time of the individual sections and decreases bottle production. Furthermore, the fact that the adjustable foot itself is connected to and a part of the conventional plunger mechanism makes removal of the plunger mechanism more difficult.
It is with respect to these considerations and other background information relative to prior art plunger mechanisms that the significant improvements of the present invention have evolved.